The National Geographic Magazine
jet propulsion rather than to drive a propeller.
But realization of the ideas of these opti
mists had to await advances in other fields,
particularly the development of efficient light
weight air compressors and high-temperature
resistant materials for turbine blades and com
bustion chambers.
My first contact with this field was the
result of a request from McCook Field to the
Bureau of Standards about 1921 for a study
of the practicability of jet propulsion. The
study was made by Edgar Buckingham, and
he concluded quite correctly that at 250 miles
per hour the fuel consumption of the most
efficient jet engine would be at least four times
as great as that of a piston engine driving a
propeller. I participated in the discussion of
the draft of the report.
My next contact was in 1941 as representa
tive of the Bureau of Standards on the NACA
Special Committee on Jet Propulsion under
the chairmanship of Prof. W. F. Durand.
This committee stimulated the military serv
ices to contract with manufacturers of steam
turbines for the development of a turbine
driven ducted fan, a small turbojet, and a
turbine driving a propeller.
However, the Germans and the British had
advanced more rapidly. The Germans had
flown a Heinkel-178 airplane powered by a
turbojet engine on August 27, 1939, and
on May 14, 1941, the British had flown a
Gloster airplane powered by the engine in
vented by that gifted Englishman, Frank (now
Sir Frank) Whittle. Not until October 2,
1942, did a U. S. airplane fly with jet power,
a copy of the Whittle engine. Not until Jan
uary 21, 1944, did one of the original U. S.
designs initiated by the Durand committee
fly as a booster engine, and on January 1,
1945, as sole power.
Whittle's earliest patent was filed on Jan
uary 16, 1930. When he submitted his en
gine to the government authorities in Great
Britain, it was rejected as inoperative. I have
heard Whittle state since that they were prob
ably correct in their judgment at the time, but
he himself did not give up.
The first German flight used an engine
developed from patents of Hans von Ohain,
who was totally unaware of Whittle's work.
Jet Engine Would Heat 6,500 Houses
A jet engine is fundamentally a device for
converting fuel into heat and then developing
thrust from that heat by squirting a jet of hot
air to the rear. Any boy who has blown up
a toy balloon and let it escape from his hands
has observed jet propulsion in action. At low
speeds the jet engine is not very efficient; the
higher the speed, the more efficient it becomes.
A recent turbojet engine, the Allison
J-71-A -1, weighs 3,650 pounds and gives a
thrust of nearly 10,000 pounds. The heat
generated is enough to heat 6,500 six-room
houses in the climate of Washington, D. C.
At 375 miles per hour, 10,000 pounds of
thrust is equivalent to 10,000 horsepower;
at 750 miles per hour, the same amount of
thrust is equivalent to 20,000 horsepower.
One of the first discoveries about jet engines
in flight was that when the airplane reached
a high altitude the "fire" in the engine often
went out, or flamed out, as the pilot would say.
Unless he could restart his engine at a lower
altitude, he had to make a forced landing.
Fortunately, at about the same time this
problem was faced, the NACA's Lewis Flight
Propulsion Laboratory in Cleveland had com
pleted new research facilities which permitted
duplicating on the ground the altitude oper
ating conditions. The NACA collaborated
with industry and the military services in the
solution of this problem, with the result that
jet engines can be operated dependably at alti
tudes more than twice as high as before this
research program began.
Ceramels-Metals Plus Ceramics
The jet engine is dependent on advances
in physics, chemistry, metallurgy, and their
applications, for combustion occurs in air flow
ing at superhurricane speed and intense heat.
To be even reasonably efficient, the jet en
gine needs to operate at temperatures ap
proaching 1,5000 F., and for the future we
should like to go to still higher temperatures,
perhaps to 3,0000 F.
To cope with such terrific heat, new mate
rials combining metals with ceramics, called
ceramels or cermets, are under study, and
methods of cooling the hot parts of the engine
are being developed.
For supersonic propulsion with turbojet
engines, it is at present necessary to augment
the thrust of the turbojet by the use of after
burning, the burning of fuel in the tail pipe
downstream of the turbine blades. There is
enough unused oxygen in the jet flow to feed
an afterburner because the combustion prod
ucts in a turbojet must be greatly diluted
with excess air to prevent destruction of the
turbine blades. We may expect afterburning
to become less and less necessary as effective
means are devised for cooling the turbine
blades or improved high-temperature materials
become available.
Other types of power for superspeed include
the rocket motor, with which sustained hori
zontal supersonic flight of a piloted airplane
was first attained by the Bell X-1.
Another source of tremendous power and
speed is the ram-jet engine, which depends
on the high speed of the aircraft or missile
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